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Unit 3 Lesson 3 Wind in the Atmosphere
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Unit 3 Lesson 3 Wind in the Atmosphere
Blow It Out!
What causes wind?
• The uneven heating of Earth’s surface by the sun
causes temperature differences in the air.
• Warm air rises, creating areas of low pressure.
Cool air sinks, creating areas of high pressure.
• Air moves from areas of higher pressure toward
areas of lower pressure.
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Unit 3 Lesson 3 Wind in the Atmosphere
What causes wind?
• Wind is the movement of air caused by
differences in air pressure.
• Cold air at the poles creates areas of high
pressure there. Warm air at the equator creates
an area of lower pressure.
• Globally, air moves in circular patterns called
convection cells. Convection cells occur at about
every 30° of latitude, producing pressure belts.
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Unit 3 Lesson 3 Wind in the Atmosphere
What causes wind?
• How does the sun contribute to global wind
patterns?
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Unit 3 Lesson 3 Wind in the Atmosphere
How does Earth’s rotation affect wind?
• Earth rotates, causing winds to be deflected, or
curved.
• The apparent curving of the path of a moving
object from an otherwise straight path due to
Earth’s rotation is called the Coriolis effect.
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Unit 3 Lesson 3 Wind in the Atmosphere
How does Earth’s rotation affect wind?
• Points on Earth closer to the equator must travel
faster than points close to the poles to make one
complete rotation each day.
• In the Northern Hemisphere, air moving to the
north curves to the east, and air moving to the
south curves to the west.
• *Winds and currents tend to flow to the right of
north of the equator
• *And to the left south of the equator
• *Responsible for the rotation of large cyclones
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Unit 3 Lesson 3 Wind in the Atmosphere
How does Earth’s rotation affect wind?
• How would the appearance of the purple arrows
(curved paths) in the diagram below change if
Earth rotated twice as fast?
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Unit 3 Lesson 3 Wind in the Atmosphere
Blowin’ Around
What are examples of global winds?
• Global winds are wind systems that occur at or
near Earth’s surface.
• The major global wind systems are the polar
easterlies, the westerlies, and the trade winds.
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Unit 3 Lesson 3 Wind in the Atmosphere
What are examples of global winds?
• The trade winds blow between 30° latitude and
the equator in both hemispheres and curve west.
• The westerlies blow between 30° and 60° latitudes
in both hemispheres and curve east.
• The polar easterlies blow between the poles and
60° latitudes in both hemispheres and curve west.
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Unit 3 Lesson 3 Wind in the Atmosphere
What are examples of global winds?
• The trade winds of both hemispheres meet in a
calm area around the equator called the
doldrums. Very little wind blows in the doldrums.
• The horse latitudes are calm areas at about 30°
latitude in both hemispheres. Air stops moving
and sinks in the horse latitudes.
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Unit 3 Lesson 3 Wind in the Atmosphere
What are examples of global winds?
• Identify the major global wind systems in the
image below.
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Unit 3 Lesson 3 Wind in the Atmosphere
What are examples of global winds?
• Jet streams are narrow belts of high-speed winds
that blow from west to east, between 7 km and
16 km above Earth’s surface.
• Jet streams follow boundaries between hot and
cold air and can shift north and south.
• The two main jet streams are the subtropical jet
stream and the polar jet stream.
• *Found in the upper troposphere
• *Common in the middle latitudes – usually from
the west
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Unit 3 Lesson 3 Wind in the Atmosphere
What are examples of global winds?
• Identify the two main jet streams in the image
below.
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Unit 3 Lesson 3 Wind in the Atmosphere
Desert Trades
• Trade winds carry dust from the Sahara across the
Atlantic Ocean.
• The Sahara is the world’s largest hot desert.
• Dust in Florida can come from the Sahara.
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Unit 3 Lesson 3 Wind in the Atmosphere
Feelin’ Breezy
What are examples of local winds?
• Local winds are the movement of air over short
distances. They can blow from any direction.
• A sea breeze forms during the day, as cooler air
over the ocean flows toward the land.
• A land breeze forms at night, as cooler air from
the land blows toward the water.
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Unit 3 Lesson 3 Wind in the Atmosphere
What are examples of local winds?
• During the day, the sun warms the air on
mountain slopes faster than it warms the air in a
valley. This results in areas of lower pressure near
the mountain tops.
• The pressure difference causes a valley breeze,
which flows from the valley up the slopes of
mountains during the day.
• At night, as air along the mountain slopes cools, it
flows down into the valley, creating a mountain
breeze.
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